The present invention relates to an aerobic waste water purification process with intermittent batchwise supply of waste water to the activated sludge tank from which treated waste water drains continuously, the waste water inlet being opened up for a short time whenever the intensity of the bacterial metabolism in the tank has dropped below a specified value.
In biological waste water purification plants, the intention is to reduce the pollution load of the waste water by bacterial degradation. Thus, carbon compounds are degraded in the aerobic waste water purification in activated sludge tanks, but in addition, in plants in which certain sludge loading ranges are not exceeded or nitrifying bacteria can be enriched, oxidation of ammonium is also possible. The following table shows sludge loading ranges which permit a simultaneous nitrification.
TABLE 1 ______________________________________ Dimensioning values for one-stage activated sludge plants with nitrification Residence time Temperature in Age of sludge BOD.sub.5 sludge of the waste activated sludge dried matter load in water for rain tank in .degree.C. in d kg/(kg .multidot. d) discharge in h ______________________________________ 5 15 0.1 approx. 5 to 12 10 7 0.2 approx. 2.5 to 6 15 4 0.3 approx. 1.5 to 4 20 3 0.4 approx. 1.5 to 3 ______________________________________
The final product of the ammonium oxidation is nitrate which is used by certain organisms as a terminal hydrogen acceptor under anoxic conditions. Since anoxic conditions occur mainly in the final clarification in conventional activated sludge plants, denitrification results at that point. Either extracellular or intracellular carbon compounds serve as electron donors for the microorganisms under these conditions.
The nitrogen liberated in this type of nitrate reduction rises in the form of small bubbles and drives the activated sludge upwardly.
Rising sludge cannot be recycled into the activated sludge tank and drains off with the purified water. Consequently, this sludge is no longer available for purifying the waste water and, in addition, considerably pollutes the receiving watercourse as a result of its strong oxygen-depleting characteristic.
An effective water process control is possible only if, as a result of a systematic process control (in relation to the elimination of nitrogen), denitrification is successfully prevented in the final clarification tank and at the same time a substantial nitrogen elimination is successfully achieved in the sludge activation.
A number of waste water purification processes attempt to satisfy this requirement by carrying out controlled denitrification. Upstream or simultaneous denitrification in one-stage activated sludge plants are conventional methods which are often employed. They often function fairly ineffectively since there is hardly any possibility of substantially affecting the process. Waste water treatment technology is more likely to offer suggestions (Boehnke et al in Korrespondenz Abwasser 1986, pages 1125-33) which are always, however, associated with considerable expense. A further possibility is offered by the carousel process (Eggert in Industrieabwasser 1985, pages 17-23) which, however, can be implemented only in plants which are to be refitted.